When off-loading containers and break-bulk cargo from large oceangoing ships (or a dock) onto a variety of lighters (and other small craft), off-loading must be accomplished in all types of weather and in the presence of high sea states. Problems arise both due to the motions of the vessels in inertial space and the motions of the vessels relative to each other.
Existing shipboard cranes use a single cable with a cargo coupling mechanism (or spreader) suspended from an overhead structure. Ship motion may force the cargo (or spreader) into pendulous action, allowing it to swing unchecked. Difficulty may be encountered when trying to mate the spreader with a container that is on the oceangoing vessel itself. Furthermore, depositing a swinging container onto a moving lighter without damage to cargo and hazards to personnel is also difficult.